Relevant prior art has attempted to develop various methods to quantify an extent of blockage of blood circulation. For example, the blockage is often seen as stenosis in a coronary artery, and the extent of blockage is quantified by a predetermined parameter or index. One such widely used index is fractional flow reserve (FFR) for indicating a physiologic significance of coronary artery stenosis.
One area of the prior art attempts directly uses measured pressure data to determine a blockage parameter in a certain blood vessel. By inserting an intracoronary pressure guide wire into a guiding catheter that was introduced to the aorta, the distal coronary pressure and the aortic pressure are measured. After calibration, the pressure guide wire is advanced into coronary artery across stenosis to the most distal artery. As the pressure guide wire tip is kept away from touching the vessel wall, the distal coronary and aortic pressures are recorded simultaneously under maximum coronary vasodilatation. Unfortunately, this measurement technique is an invasive procedure as the pressure wire needs to be inserted into the coronary artery across stenosis and bears some risk.
Another area of the prior art attempts estimates the FFR from a ratio of a coronary blood flow to a total arterial lumen volume based upon angiographic image data. Unfortunately, in order to quantify the total arterial lumen volume and an associated coefficient, complicated processing procedures are required.
Yet another area of the prior art attempts utilizes angiographic image data in order to study blood circulation. In some attempts, time-density curves (TDCs) or time-intensity curves (TICS) are constructed for selected regions of interest (ROIs) from the angiographic image data. Based upon the TDCs or TICs, the blood circulation level is compared among the selected regions. In some of the angiography imaging techniques, although TDCs are generated from the angiographic images, the TDCs reflect density changes in selected regions or tissues rather than individual blood vessels as ROI. On the other hand, a blood flow speed or a rate of change in blood flow speed is evaluated based upon angiographic image data in individual coronary arteries in one angiography imaging technique, and the blood flow speed is determined based upon a distance traveled along a particular artery by the contrast agent over time. That is, the blood flow speed is determined directly from the visual identification of the contrast agent along a blood vessel without the use of time-density data such as TDCs.
In view of the above prior art techniques, it remains desirable to implement a clinical index that is useful in evaluating stenosis in a particular blood vessel so as to objectively determine if a certain medical procedure should be performed on a patient.